The invention relates to a printing-plate changer assembly for making ready and feeding printing plates to a plate cylinder of a printing unit, the assembly including a printing-plate changer located upline or in front of the printing unit, in a position for feeding the printing plates, and being articulatedly connected to the printing unit by at least two four-bar linkages so that it is pivotable upwardly into a swung-away position for servicing work.
A printing-plate changer of the foregoing general type has become known heretofore from the published European Patent Document EP 0 433 798 A2. This printing-plate changer is fixed to a lower portion of a printing unit guard and is pivotable upwardly together with the latter by two four-bar linkages. A disadvantage of this printing-plate changer is that a locking mechanism is required for the aforementioned positions, which must be locked and unlocked, respectively, separately by mechanical or electrical control or by hand. This applies particularly to the swung-away position located at the top, because the performance of service work calls for a high level of safety. In addition, the action of pivoting into the upper end position requires an expenditure of a great amount of force.
It is accordingly an object of the invention to provide a printing-plate changer assembly of the type described at the introduction hereto that is held securely and automatically in the positions thereof and is easily bringable into the swung-away position.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a printing-plate changer assembly for making-ready and feeding printing plates to a plate cylinder of a printing unit, the assembly including a printing-plate changer located upline of the printing unit, in a position for feeding the printing plates, and being articulatedly connected to the printing unit by at least two four-bar linkages so that it is pivotable upwardly into a swung-away position for servicing work, comprising at least one element articulatedly connected with the printing unit and with the printing-plate changer so that it holds the printing-plate changer in both the feeding and the swung-away positions and assists the pivoting movement.
In accordance with another feature of the invention, the at least one element is formed as a sprung element and is articulated and aligned offset with respect to the articulations of the four-bar linkages, so that it urges the printing-plate changer downwardly into the position for feeding the printing plates and upwardly into the swung-away position, as well as away from a given pivoting angle.
In accordance with a further feature of the invention, a plurality of the elements are disposed on both sides of the printing-plate changer.
In accordance with an added feature of the invention, the at least one element is a gas pressure spring.
In accordance with an additional feature of the invention, the printing-plate changer serves to replace a printing unit guard, and the printing unit is accessible for substantially all servicing work due to the pivoting action.
In accordance with yet another feature of the invention, the printing-plate changer assembly includes an active element for performing the pivoting movement.
In accordance with yet a further feature of the invention, the printing-plate changer assembly includes two upper levers and two lower levers for providing articulation.
In accordance with yet an added feature of the invention, the printing-plate changer has a substantially two-dimensional extent, and the assembly includes a plurality of articulations formed so that the printing-plate changer completes the pivoting in a semicircle lying in the plane of the two-dimensional extent of the printing-plate changer.
In accordance with yet an additional feature of the invention, the printing-plate changer has a substantially two-dimensional extent, and the assembly includes a plurality of articulations formed so that the printing-plate changer completes the pivoting in a semicircle lying perpendicularly to the plane of the two-dimensional extent of the printing-plate changer.
In accordance with still another feature of the invention, the printing-plate changer assembly includes a synchronization shaft for connecting at least one lever pair to another at an articulation.
In accordance with still a further feature of the invention, the printing-plate changer is also constructed for holding the printing plates after they have been used.
In accordance with still an added feature of the invention, power is introducible into the printing-plate changer in a region of the axes of rotation.
In accordance with still an additional feature of the invention, power is introducible via at least one clutch.
In accordance with an alternative feature of the invention, power is introducible via gearwheels intermeshing in a closed state.
In accordance with another feature of the invention, the printing-plate changer assembly includes a locking device for securing the intermeshing of the gearwheels.
In accordance with a further feature of the invention, the printing-plate changer assembly includes a printing-plate conveying device disposed in the printing-plate changer.
In accordance with an added feature of the invention, the printing-plate conveying device has a pressure roller and a back-pressure roller which are pressable against one another by spring force, with a printing plate included therebetween.
In accordance with an additional feature of the invention, the printing-plate changer assembly includes a motor for driving the printing-plate conveying device, the motor being disposed on the printing unit.
In accordance with a concomitant feature of the invention, the printing-plate conveying device has a free wheel for permitting a printing plate to be drawn in by rotation of the plate cylinder.
Thus, the object is achieved in that at least one element is constructed and articulated on the printing unit and printing-plate changer so that it holds the printing-plate changer in both positions and assists the pivoting movement.
Printing-plate changers in this sense can be automatic, semi-automatic or also make-ready devices for improved manual feeding.
Due to the configuration according to the invention of the printing-plate changer, a secure hold in all positions is achieved. In particular, assurance is provided that the printing-plate changer remains in the upper swung-away position thereof even when vibration occurs. As a result, in particular, work safety during servicing work is increased in a simple and reliable manner, and there is no requirement for a separate locking device with separate locking and/or unlocking, particularly in the swung-away position. Due to the assistance provided to the pivoting movement, the printing-plate changer according to the invention is particularly suitable for manual operation. However, performing the pivoting movement automatically is also possible, of course. In this case, a less powerful drive is required. The printing-plate changer and the pivoting mechanism are of compact construction, and a synchronous movement sequence and weight compensation are possible in a simple manner.
One embodiment of the invention provides for the element to be formed as a sprung element and to be articulated and aligned offset with respect to the articulations of the four-bar linkages so that it urges the printing-plate changer downwardly into the position for feeding the printing plates and upwardly in the swung-away position, as well as from a specific pivoting angle. The elements can be arranged on both sides of the printing-plate changer. The sprung element is expediently a gas pressure spring or strut, because this offers the additional advantage that the movement sequence is damped. This is particularly advantageous when the printing-plate changer is pivoted into the lower position thereof, because this movement sequence is assisted by the weight, and the printing-plate changer should be prevented from sharply striking the printing unit.
The printing-plate changer is advantageously constructed so that it completely replaces the printing unit guard, provision being made for such a pivoting action that, thereby, the printing unit is accessible for virtually all servicing work. In this manner, a separate printing unit guard can be completely dispensed with.
If the printing-plate changer is also particularly suitable for manual operation, due to the compact construction thereof and due to the assistance thereby to the pivoting movement, it is nevertheless possible for an additional active element to be provided which performs the pivoting movement.
The at least two four-bar linkages can be configured so that the articulation is provided by two upper levers and two lower levers. The articulation can be formed so that the printing-plate changer completes the pivoting action in a semicircle which lies in the plane of the two-dimensional extent of the printing-plate changer. In this case, the axes of the articulations are perpendicular to this plane, and the pivoting movement goes to the side and then upwardly in a semicircle so that the levers complete a pivoting movement through about 180xc2x0.
Another embodiment provides for the articulations to be formed so that the printing-plate changer completes the pivoting action in a semicircle which lies perpendicular to the plane of the two-dimensional extent of the printing-plate changer. In this case, the axes of the articulations extend in the plane of the printing-plate changer, and ensures that at least one pair of levers in an articulation is connected to another by a synchronization shaft. In this way, a synchronous movement sequence is ensured over the entire width of the printing-plate changer. The levers are pivoted through about 180xc2x0 in this embodiment as well.
In both of the aforementioned exemplary embodiments, the pivoting angle due to which the sprung element urges the printing-plate changer upwardly is determined in accordance with the articulation of the changer. The offset of the articulation of the sprung element with respect to the articulations of the levers is expediently such that a force component is produced upwardly the instant the printing-plate changer has been pivoted through 90xc2x0, so that the assistance to the pivoting movement by the sprung element begins from this instant of time. This offset of the articulations also includes such an oblique positioning of the sprung element that the latter runs obliquely from bottom to top when the levers are in a horizontal position and, consequently, the force component can be developed upwardly. This is expedient precisely when the printing-plate changer is pivoted manually, because the upper range of the pivoting action is more laborious to perform manually.
A further development of the printing-plate changer provides for the latter also to be constructed so as to hold the printing plates after they have been used. For this purpose, a used printing plate is pushed by the plate cylinder into an ejection shaft of the printing-plate changer for used printing plates and then, if appropriate, is taken over by a withdrawal clip, which pulls the used printing plate completely out of the printing machine, so that the printing plate is stored in the ejection shaft for removal.
Power is expediently introduced into the printing-plate changer in the region of the axes of rotation, it being possible for the power to be introduced electrically or mechanically. The arrangement in the region of the axes of rotation is expedient in particular for cables or for compressed air or hydraulic hoses. However, the mechanical introduction of power can also be performed via a clutch or coupling. The advantage of the mechanical, pneumatic or hydraulic introduction of power is that no motor has to be arranged in the printing-plate changer, and the latter can therefore be of more lightweight construction. The motor can be provided at a different location in the printing machine.
An embodiment of a clutch calls for power to be introduced via gearwheels which intermesh in the closed state. For the case wherein the gear mechanism forces pressing the gearwheels apart are too great for the sprung element, provision can be made for the position of the printing-plate changer to be secured, in the closed state, by an additional locking device. However, this merely has a supporting function and not a function specific to safety, as in the prior art mentioned at the introduction hereto.
A printing-plate conveying device can be arranged in the printing-plate changer, and can be supplied with power in the manner mentioned above. One possibility of configuring the printing-plate delivery device is that a pressure roller and a back-pressure roller are pressed against one another by spring force, including a printing plate, so that the printing plate is conveyed by the rotation of the rollers. The printing-plate conveying device can then be driven by a motor arranged on the printing unit. The printing-plate conveying device expediently has a free wheel, which permits the printing plate to be drawn in by rotation of the plate cylinder. This is expedient, because the leading edge of the printing plate is gripped by a clamping device of the plate cylinder and further conveyance is then intended to be performed by rotation of the plate cylinder, in order to wind the printing plate cleanly around the latter.
Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in a printing-plate changer assembly, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: